Change static to const.
Change static to const.

This commit

  https://github.com/rust-lang/rust/commit/f35f973cb700c444d8c029ee13b37dc16d560225

changes `static`s to `const`s in quite a few places in libunicode.

For some reason, this causes rustc to dump its core, which is in itself a bug,
but here we can fix it by changing some static variables to const.

golddranks/regex,edunham/regex,bluss/regex,SeanRBurton/regex,bluss/regex,rust-lang/regex,edunham/regex,rust-lang-nursery/regex,rust-lang-nursery/regex,edunham/regex,rust-lang/regex,rust-lang-nursery/regex,SeanRBurton/regex,rust-lang/regex,rust-lang-nursery/regex,bluss/regex,rust-lang/regex,golddranks/regex,golddranks/regex,rust-lang/regex,SeanRBurton/regex,SeanRBurton/regex,rust-lang-nursery/regex,SeanRBurton/regex